1. Field of the Invention
This invention relates to a belt driven continuously variable transmission, especially relates to a belt driven continuously variable transmission suitable for using in an automatic variable transmission to be mounted on an automobile, in detail, relates to a pressure regulating mechanism section generating an axle force corresponding to a transmission torque.
2. Description of Prior Art
Generally, A V-Belt type continuously variable transmission (CVT) has a primary pulley and a secondary pulley each of which is made up of a movable sheave and a stationary sheave. Metallic belt is wound around both of these pulleys. A shifting operation is done at a required moment by moving the movable sheave with a hydraulic pressure piston.
Therefore, the continuously variable transmission, where a hydraulic pressure is used, needs an oil pump and a hydraulic pressure passage. This structure makes the device not only large and complicated but also unfavorable for the transmission efficiency and the belt endurance because the structure generates the pressing force more than needed, which furthermore, makes it impossible to transmit, as the belt pressing force becomes short in supply, when the hydraulic pressure decreases by some reasons.
The applicant of the present invention has proposed a belt driven continuously variable transmission 30', as shown in FIG. 5, to wind a metallic belt 33 around a primary pulley 31 and a secondary pulley 32, whose movable sheave 31b and 32b are moved axially by actuator mechanisms 35 and 36 such as ball thread mechanism, and to arrange a pressure regulating cam mechanism 34' giving an axial force which corresponds to a transmission torque to a primary sheave 31a. (refer to the Japanese Laid Open Patent No.62-13853)
In the belt driven continuously variable transmission 30', both the sheaves 31a and 31b of the primary pulley 31 are supported on the primary shaft 30b, the pressure regulating cam mechanism 34' is supported on a boss section `a` of a stationary sheave 31a and also supported on a case by a bearing 1'.
Therefore, in the continuously variable transmission 30', a torque from the primary shaft 30b is transmitted to the stationary sheave 31a through the pressure regulating cam mechanism 34' and also transmitted from the primary pulley 31 to the secondary pulley 32 through a belt 33. When the torque is transmitted form the pressure regulating cam mechanism 34' to the stationary sheave 31b, not only a torque to be transmitted through the pressure regulating cam mechanism 34', or a fixed-side race 34'a, a roller 34'b and a movable-side race 34'c, but also another torque to be transmitted directly by the friction of the fixed-side race 34'a and a stationary sheave 31a, is produced.
A torque made by the friction varies largely because the pulley 31 is supported through the pressure regulating cam mechanism 34', so that the radial force between the sheave 31a and the boss section `a` alters according to the belt tension. For example, generally, supporting the ratio of the whole torque to be transmitted is (ten), the ratio of a torque transmitted through the fixed-side race 34'a, a roller 34'b and a movable-side race 34'c (eight) and the ratio of a torque transmitted by the frictional force between the fixed-side race 34'a and the fixed-side sheave 31a (two), the ratio of the frictional force torque can be increased from (two) to around (five) by the variation of the belt tension. Therefore, the transmission torque through the pressure regulating cam mechanism 34' also varies, so that the pressing force working on the belt 33 is made uneven. To overcome this uneveness requires a pressure regulating cam mechanism which generates a large axial force in order to keep a certain pressing force, which lowers the endurance and the transmission efficiency of the V-belt 33.
This invention is purposed to provide a belt driven continuously variable transmission which transmits whole torque through a regulating cam mechanism so that the belt pressing force which responds correctly to the transmission torque can be obtained.